Download 3.1 Classifying Chemical Compounds

Bonding is the interaction between the
valence electrons of atoms.
 When atoms exchange electrons, they
form an ionic bond.
 When atoms share electrons, they form a
covalent bond.
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Based on physical properties,
compounds can be classified into 2
groups: ionic and covalent.
When two atoms form a bond, each
atom attracts the other atom’s electrons
in addition to its own.
 The electronegativity (EN) of an atom is
a measure of an atom’s ability to attract
electrons in a chemical bond.
 Each element has an EN value.
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As atomic size decreases from left to right
across a period, EN increases.
› The smaller the radius of an atom, the more
proton attraction it has. Thus its EN value is
higher.

Similarly, as the atomic size increases going
down a group the EN value decreases.
The differences between EN values is used
to decide whether the bond between two
atoms is ionic or covalent.
 The symbol Δ EN stands for the difference
between two electronegativity values.
 When calculating the Δ EN, the smaller EN is
always subtracted from the larger EN, so
that the Δ EN is always positive.
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P 74 # 1- 6 McGraw Hill
 P 60 # 1 – 8 Nelson
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